Focusing attention on optical switches, optical switches are installed for example in nodes in a ring network constituting a Dense Wavelength Division Multiplexing (DWDM) optical communication network. Most of the optical switches installed at such nodes mechanically place and remove optical elements such as prisms or mirrors in and from light paths to change light paths. Optical switches that change light paths are used as Reconfigurable Optical Add/Drop Multiplexers (ROADMs) capable of selecting or reconfiguring light wavelengths to be dropped or added at the nodes. Optical switches can also be used as backup devices during maintenance and inspection services or failure recovery in redundant systems having a dual signal system consisting of a light path that is normally in actual use (production path) and a backup light path (backup path) that can be switched into service at long intervals. Some of these optical switches are formed on a chip in which optical and driving systems are formed as an integral piece in MEMS device fabricated by using semiconductor micromachining technology because they are provided to switch microstructure optical paths.
Optical switches shown herein are microscopic MEMS devices and include moving parts that are essential to their function. Therefore the mechanical reliability of the moving parts is especially crucial. Required mechanical reliability includes switching durability to withstand frequent switching of light paths and the switching reliability of switching operation performed after a long idle period. For example, in the case of optical switches used as above-mentioned ROADMs, an optical signal flow will frequently change, given the fact that the optical line is shared on a wavelength or time basis. Accordingly, the frequency of switching operations of a optical switch increases, which requires a high switching durability. Switching durability is also essential to optical switches used in a monitoring system that involves switching between a main signal and a monitor signal on an as needed basis. On the other hand, optical devices used as backup devices in a redundant system as mentioned above, the switching frequency is very low. Specifically, switching from a production system to a backup system may be done when the inspection or maintenance of the production system is performed, for example once a year. Therefore, the reliability of switching after a long idle period is required.
Ensuring the mechanical reliability of MEMS devices typified by optical switches which have moving parts is absolutely essential. A related-art technique for improving the mechanical reliability is a optical switch subsystem disclosed in Japanese Patent Application Laid-Open No. 2004-48187. The optical switch subsystem uses a rough motion mode or fine motion mode of the angle of mirrors as modes for controlling a optical switch, which is an MEMS device, to obtain the results of measurements of the intensity of light from a light source when a light beam from the light source is switched by the optical switch, conducts self-diagnosis based on the measurements, conducts self-diagnosis based on switching time, and performs calibration based on the result of the self-diagnosis. The document states that a switching failure can be detected through the diagnosis and the reliability and performance of an optical communication system can be improved.
However, the related art described above requires an additional light source and receiving optics (a light intensity monitor) dedicated to the self-diagnosis of the optical switch. Thus, optical switches capable of conducting self-diagnosis are equipped with an increased number of components.
Furthermore, the related-art technique is a system incorporating a optical switch premised on correction of control inputs and therefore is not applicable to optical switches currently on the marketplace that are not premised on correction of control inputs.